A traveling wave tube, a klystron or the like are electron tubes to be used for performing amplification, oscillation or the like of a high-frequency signal by interaction between an electron beam formed by an electron gun and a high-frequency circuit.
In Patent Literature 1 (PTL1), there is disclosed a traveling wave tube 100 as illustrated in FIG. 3. The traveling wave tube 100 includes an electron gun 102 that forms an electron beam 101, a helix electrode 105, which is a high-frequency circuit that makes the electron beam 101 formed by the electron gun 102 and a high-frequency signal (microwave) interact with each other, and a collector electrode 106 that collects the electron beam 101 outputted from the helix electrode 105 (Referring to PTL1).
The electron gun 102 includes a cathode electrode 103 that forms thermal electrons, and a heater 104 that supplies heat energy for forming thermal electrons to the cathode electrode 103.
The electron beam 101 formed by the electron gun 102 is accelerated by an electric potential difference between the cathode electrode 103 and the helix electrode 105, and is introduced into the helix electrode 105. Then, the electron beam 101 proceeds through the inside of the helix electrode 105 while interacting with high-frequency signals inputted from an end of the helix electrode 105. The electron beam 101 that has passed through the inside of the helix electrode 105 is collected by the collector electrode 106.
A power supply device includes: a helix power supply 107 that supplies to the cathode electrode 103 a helix voltage (Ehel), which is a negative direct-current voltage on the basis of the electric potential (HELIX) of the helix electrode 105; a collector power supply 108 that supplies to the collector electrode 106 a collector voltage (Ecol), which is a positive direct-current voltage on the basis of the electric potential (H/K) of the cathode electrode 103; and a heater power supply 109 that supplies to the heater 104 a heater voltage (Eh), which is a negative direct-current voltage on the basis of the electric potential (H/K) of the cathode electrode 103.
In the electron gun of such structure, it is made such that thermal electrons are formed easily from the cathode electrode 103 by heating the cathode electrode 103 by the heater 104.
However, there is an issue that an amount of formed electrons decreases (that is, an amount of electron beams decreases) due to long-term deterioration of a cathode electrode by long term use even if a heater current, a helix voltage value, a collector voltage value or the like are driven on the same conditions.
About such issue, there is proposed in Patent Literature 2 (PTL2) a technology in which an amount of formed electrons is monitored, and the cathode temperature is made to rise by increasing a heater current based on a monitoring result, thereby compensating decrease in the amount of formed electrons. Patent literature 3 (PTL3) relates to setting of an operating temperature of a Shottkey emission electron gun. In PTL 3, there is disclosed that an operating temperature is determined in such a way that a Shottkey emission electron current set in advance is obtained at a predetermined extraction voltage. In addition, in PTL3, there is proposed that a Shottkey emission chip of an electron gun is heated for a short time to the above-mentioned operating temperature or more in order to improve cleanliness of the Shottkey emission chip.